2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
522
1. Before the start of COST 730, the need for use of an advanced multi-node thermo-
physiological model as basis for the UTCI was recognised. Although several such
models have been developed to date (Stolwijk, Nadel et al. 1973; Wissler 1985; Tanabe,
Arens et al. 1994; Fiala, Lomas et al. 1999; Fiala, Lomas et al. 2001; Havenith 2001;
Huizenga, Hui et al. 2001; Tanabe, Kobayashi et al. 2002; Fiala, Lomas et al. 2003;
Ghaddar, Ghali et al. 2003), not all models were available for evaluation. The two
models evaluated in detail were those from Fiala and Tanabe.
2. These two models gave comparable results for climates at or near to comfortable
conditions and for 50% relative humidity. However outside such conditions, the Fiala
model gave better predictions of the human response.
3. The UTCI model requires accurate prediction of the average human thermophysiological
response for all possible weather conditions. Extensive validation of the
now 340-node Fiala model (one of the most advanced multi-node thermo-physiological
models available) has demonstrated its ability to predict core and local skin
temperatures and sweat rates for people of average fitness over a large range of
conditions. After extensive discussion of the Working Group 1 experts in COST 730, a
decision has been reached that the group is now satisfied with this model’s performance
in the main application range of the UTCI. For special climates with local risks
(frostbite) additional work may be required.
4. How the model output shall be transformed into an index is a crucial part of the
future UTCI model. This transformation could be a single index equation or various
equations depending on the domain.
5. In order to help the general public to relate directly to the UCTI, it is proposed that
this index should be on the temperature scale (e.g. in degrees Celsius). In this way the
influence of factors such as wind and sunshine should be easy to understand, causing
the temperature felt to be x °C cooler or warmer than without these factors.
6. As the UTCI should represent the average conditions of a human within a given
climate, a reference person shall need to be defined. The reference person proposed has
a metabolic rate of 135 W/m2 while walking at 4 km/h . The wind speed should account
for this walking speed in accordance with ISO 9920. Wind direction is assumed to be
undefined in relation to walking direction.
7. Clothing worn
7.1. Human choice/adaptation of clothing worn
People tend to adapt their clothing depending on the weather conditions, although this is
partly influenced by culture and race which varies from country to country. Thus the
UTCI should take these regional differences and adaptations into account. For instance,
on a hot summer day, typically less clothing with a low thermal insulation is worn, with
possibly more areas of the body being exposed directly or indirectly to sunlight.
However, in winter people tend to wear much more clothing with a higher thermal
insulation. Particularly under very cold conditions, more exposed areas of the body such
as the head and face should be protected from any wind as this can cause the effective
air temperature to drop dramatically, thus increasing the heat loss of the skin to the
environment and can even lead to sudden cold injury. Therefore wind protection
becomes very important under such conditions. Under wet conditions people tend to
wear rain protection which increases the overall water vapour resistance of the clothing.
For the UTCI, which clothing is worn could be based on an expert assessment and on a
continuous scale, in terms of amount of insulation and amount of body coverage.